US20090087992A1 - Method of minimizing via sidewall damages during dual damascene trench reactive ion etching in a via first scheme - Google Patents
Method of minimizing via sidewall damages during dual damascene trench reactive ion etching in a via first scheme Download PDFInfo
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- US20090087992A1 US20090087992A1 US11/863,746 US86374607A US2009087992A1 US 20090087992 A1 US20090087992 A1 US 20090087992A1 US 86374607 A US86374607 A US 86374607A US 2009087992 A1 US2009087992 A1 US 2009087992A1
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- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
- H01L21/3105—After-treatment
- H01L21/311—Etching the insulating layers by chemical or physical means
- H01L21/31144—Etching the insulating layers by chemical or physical means using masks
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- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02041—Cleaning
- H01L21/02057—Cleaning during device manufacture
- H01L21/0206—Cleaning during device manufacture during, before or after processing of insulating layers
- H01L21/02063—Cleaning during device manufacture during, before or after processing of insulating layers the processing being the formation of vias or contact holes
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- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/027—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34
- H01L21/033—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising inorganic layers
- H01L21/0334—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising inorganic layers characterised by their size, orientation, disposition, behaviour, shape, in horizontal or vertical plane
- H01L21/0337—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising inorganic layers characterised by their size, orientation, disposition, behaviour, shape, in horizontal or vertical plane characterised by the process involved to create the mask, e.g. lift-off masks, sidewalls, or to modify the mask, e.g. pre-treatment, post-treatment
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- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/027—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34
- H01L21/033—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising inorganic layers
- H01L21/0334—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising inorganic layers characterised by their size, orientation, disposition, behaviour, shape, in horizontal or vertical plane
- H01L21/0338—Process specially adapted to improve the resolution of the mask
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- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
- H01L21/3105—After-treatment
- H01L21/311—Etching the insulating layers by chemical or physical means
- H01L21/31105—Etching inorganic layers
- H01L21/31111—Etching inorganic layers by chemical means
- H01L21/31116—Etching inorganic layers by chemical means by dry-etching
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
- H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
- H01L21/768—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics
- H01L21/76801—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing
- H01L21/76802—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing by forming openings in dielectrics
- H01L21/76807—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing by forming openings in dielectrics for dual damascene structures
- H01L21/76808—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing by forming openings in dielectrics for dual damascene structures involving intermediate temporary filling with material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
- H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
- H01L21/768—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics
- H01L21/76801—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing
- H01L21/76802—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing by forming openings in dielectrics
- H01L21/76814—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing by forming openings in dielectrics post-treatment or after-treatment, e.g. cleaning or removal of oxides on underlying conductors
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
- H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
- H01L21/768—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics
- H01L21/76801—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing
- H01L21/76802—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing by forming openings in dielectrics
- H01L21/76816—Aspects relating to the layout of the pattern or to the size of vias or trenches
Definitions
- the present invention relates generally to the field of semiconductors, particularly to manufacturing methods for fabricating semiconductor devices, and more particularly to the Back-End-Of-Line (BEOL) semiconductor manufacturing process using via first dual damascene processes.
- BEOL Back-End-Of-Line
- the semiconductor manufacturing process when likened to an assembly line, includes two major components, namely the Front-End-of-Line (FEOL) which includes the multilayer process of the actual forming of semiconductor devices (transistors, etc.) on a semiconductor substrate, and the Back-End-Of-Line (BEOL) which includes the metallization after the semiconductor devices have been formed.
- FEOL Front-End-of-Line
- BEOL Back-End-Of-Line
- semiconductor devices in a microchip such as an integrated circuit (IC) need to be electronically connected through wiring.
- IC integrated circuit
- such wiring is done through multilayer metallization on top of the multilayered semiconductor devices formed on the semiconductor substrate.
- each metallization layer designated as Metal 1 , Metal 2 , so on, where Metal 1 is the metallization layer closest to the underlying semiconductor devices to provide local connections among neighboring devices, and other metallization layers provide increasingly global connections from Metal 2 to the top metallization layer.
- Each metallization layer consists of a grid of metal lines sandwiched between dielectric layers for electrical integrity. Modern semiconductor manufacturing process can involve six or more metallization layers.
- dual damascene scheme forms vias and trenches for metal interconnect simultaneously.
- FIGS. 1-5 One such scheme is shown in FIGS. 1-5 , where the process steps used to create a dual damascene interconnect structure using the via-first process scheme and the problems attendant thereto are shown.
- FIG. 1 shows a schematic cross section of a series of layers formed in the manufacture of an IC 10 prior to formation of vias therein.
- the wafer 10 's layers include a substrate 11 , metal lines 13 , an etch stop layer 20 , a low-k dielectric layer 16 , an oxide hard mask 14 , an anti-reflective coating 15 , and a photo-resist 17 .
- a via 12 is formed therein as shown in FIG. 2 .
- the photo-resist 17 , the anti-reflective coating 15 is removed. This etching causes initial damage to the via sidewalls 32 .
- FIG. 3A shows a portion of an IC 10 having a slightly more complex arrangement of layers than that of FIGS. 1 and 2 , where the via 12 has already been etched by the processes described above.
- This via 12 has been etched through an oxide hard mask 14 , an inter-level dielectric layer (IDL) 16 (possibly a low-k or ultra low-k dielectric), and partially into the etchstop layer 20 with the IDL 16 .
- the integration layer 18 is particularly necessary when using low-k or ultra low-k materials for the IDL 16 for better adhesion and reliability.
- the via 12 is filled with an organic planarizing layer (OPL) 22 , which fills the via 12 and covers the hard mask 14 .
- OPL organic planarizing layer
- OPL layer 22 Over the OPL layer 22 is formed a oxide-like overlayer (OLO) 24 , an anti-reflective coating 26 , and a photo-resist 28 .
- OLO oxide-like overlayer
- a pattern 30 for a trench is formed in the photo-resist 28 .
- the result of formation of the vias and trenches on the wafer 10 are both horizontal and vertical via chains as shown in FIGS. 2B and 2C .
- FIG. 3B shows the effect of etching using a CF 4 chemistry.
- the anti-reflective coating 26 and the OLO 24 are etched through as well as a portion of the OPL 22 .
- the photo-resist 28 and anti-reflective coating 26 are removed and the OPL 22 is removed to a level below the oxide hard mask 14 using organic chemistry such as O 2 , CO 2 , H 2 or N 2 based chemistry, as shown in FIG. 3C .
- organic chemistry such as O 2 , CO 2 , H 2 or N 2 based chemistry
- the oxide hard mask 14 is opened to the size of the eventual trench.
- This is sometimes called a hard mask burn and can be accomplished by a fluorine based chemistry including for example, C 4 F 8 /Ar, CF 4 /CH 2 F 2 /Ar, CF 4 /CHF 3 /Ar, etc.
- the sidewall of the via 12 is exposed to an even greater extent during this hard mask burn. This exposure of the sidewall 32 during the hard mask burn and subsequent steps effects the make up of the sidewall 32 and has a detrimental effect on the manufacture of the semiconductor.
- a main etch is undertaken where the trench 34 is formed. This is typically done using, for example, a CF 4 /Ar based chemistry. Again as a result of this step more of the sidewall 32 is exposed, which damage the sidewall 32 .
- the OPL layer 22 is finally removed in its entirety using an O 2 or H2 based chemistry. This step alone causes great damage to the sidewall 32 .
- FIG. 3G the etchstop layer 20 in the bottom of the via 12 is removed using a CF 4 or CH 2 F 2 based chemistry to complete the trench 34 and via 12 .
- DHF dilute hydrogen fluoride
- FIG. 7 c is a schematic representation of the wafer 10 following final etch stop 20 removal and DHF clean showing the undercut of the hard mask 14 .
- the undercut is produced at least in part by the ultimate removal of the ILD 16 which has been damaged by the etching processes.
- FIG. 4 is a photograph of the undercut of the hard mask 14 over the sidewall 32 of the via 12 , also called undercut.
- Much of this undercut is the result of removal of carbon depletion layer by DHF clean which is actually caused by the etching processes and is particularly troublesome when in low-k and ultra low-k dielectric applications and results in an increase in dielectric constant in the IDL 16 .
- FIG. 5 and FIG. 6 show the unprotected via sidewall after OPL layer 22 etch and following final etchstop 20 removal plus DHF clean in FIG. 6 .
- the undercut itself is a problem because it causes problem for the barrier layer deposition and hence prevents Cu from properly bonding to the via 12 sidewalls 32 .
- This problem is shown in FIG. 7D .
- This improper bonding results in device reliability issues for devices manufactured using this process. Accordingly, there is a need for a dual damascene process that will overcome the shortcomings of the currently used processes such as those discussed above.
- One aspect of the present invention is directed to a method of minimizing undercut of a hard mask in an integrated circuit (IC) structure including steps of providing an IC structure having a substrate, a interlayer dielectric layer, and a hard mask, forming a via in said IC structure, and depositing an organic planarizing layer (OPL) over the IC structure such that it fills the vias formed therein.
- IC integrated circuit
- the method also includes steps of forming a masking structure layer over the OPL, forming an opening in the masking structure that has a critical dimension (CD) smaller than an opening design dimension, anisotropic etching the OPL such that sidewall of the via remains covered with the OPL while forming a trench, and removing any remaining OPL on the sidewalls and trench, wherein the undercut of the sidewalls with respect to the hard mask is minimized by the covering of OPL during the anisotropic etching process.
- CD critical dimension
- FIG. 1 is a schematic view of an IC prior to via etch
- FIG. 2 is a schematic view of an IC following via etch using known techniques
- FIGS. 2B-2C show horizontal and vertical via chains formed in an IC
- FIGS. 3A-3G are a schematic representation of an IC undergoing dual damascene processing using known techniques
- FIG. 4 is a photograph of a trench and via formed using dual damascene techniques, showing a hard mask undercut
- FIG. 5 is a photograph of a via and trench structure after OPL etch with no protection of the via sidewall
- FIG. 6 is a photograph of a via and trench structure with bad undercut
- FIG. 7 a is a schematic representation of an IC showing a via structure formed using known techniques following further deposition OPL, OLO, anti-reflective layers, lithography of a photo resist layer and finish the dual damascene photo masking;
- FIG. 7 b is a schematic representation of the IC of FIG. 7 a following etching, showing damaged ILD layer on the sidewalls of the trench and via structures;
- FIG. 7 c is a schematic representation of a via and trench structure formed using known techniques and having a hard mask undercut caused by removal of the damaged layer by dilute hydrogen fluoride (DHF) clean shown in FIG. 7 b;
- DHF dilute hydrogen fluoride
- FIG. 7 d is a schematic representation of a via and trench structure showing the problem area for barrier metallization
- FIG. 8 is a schematic view of an IC undergoing a first step in the method of the present invention with the CD decreased approximately 20% from the design dimension;
- FIG. 8 a is a schematic view of an IC undergoing a first step in a method of the present invention with the CD decreased by a taper formed in the OLO layer.
- FIG. 9 is a schematic view of an IC undergoing a second step in the method of the present invention.
- FIG. 9 a is a schematic view of an IC undergoing a second step in a method of the present invention with the CD decreased by a taper formed in the OLO layer;
- FIG. 10 is a schematic view of an IC undergoing a third step in the method of the present invention.
- FIG. 11 is a schematic view of an IC undergoing a fourth step in the method of the present invention.
- FIG. 12 is a schematic view of an IC undergoing a fifth step in the method of the present invention.
- FIG. 13 is a schematic view of an IC after undergoing a sixth and final step with dilute hydrogen fluoride (DHF) clean in the method of the present invention
- FIG. 14 is a schematic view of a trench only portion of an IC undergoing the first step of the method of the present invention with the CD reduced by at least 20% from the design dimension;
- FIG. 15 is a schematic view of a trench only portion of an IC undergoing the second step of the method of the present invention where the OPL layer is over etched, removing any footing at the bottom of the OPL and creates an opening for the trenches which actually compensates for the reduction of CD at OLO step;
- FIG. 16 is a schematic of a trench only portion of an IC after undergoing etching, ashing, and etch stop removal showing damaged areas in the sidewall of the trench;
- FIG. 17 shows the trench only portion of FIG. 17 following dilute HF cleaning to remove the damaged portion of the ILD layer
- FIG. 18 is a schematic view of a trench only portion of an IC undergoing the first step of the method of the present invention with the CD reduced by a tapered OLO layer.
- FIG. 19 is a schematic view of a trench only portion of an IC undergoing the second step of the method of the present invention where the OPL layer is over etched to compensate for the reduction in CD caused by a tapered OLO layer.
- one aspect of the present invention is directed to a scheme which protects the sidewalls during the trench reactive ion etch (RIE) process, in a via first dual damascene process.
- RIE trench reactive ion etch
- an etch sequence is used on masking structure for example an oxide-like over-layer (OLO) and an OPL integration scheme where the via sidewalls closest to the trench are protected by the OPL during OPL etch, an oxide hard mask open and main etches to avoid any unnecessary exposure to the sidewalls.
- OLO oxide-like over-layer
- this process does not affect the CD of trench only structures, having no via sidewalls to be concerned with.
- FIG. 8 shows a cross section of a portion of an IC 10 in which vias 12 have already been formed.
- the portion of the IC 10 includes a substrate 11 , on which metal lines 13 have been formed.
- An etch stop layer 20 covers the metal lines 13 and the substrate 11 .
- a ILD layer 16 covers the etch stop layer 20 and into which vias 12 have been formed, as described above with respect to FIGS. 1 and 2 .
- the vias 12 are filled with an OPL layer 22 .
- the top of the ILD layer 16 is covered with a hard mask 14 .
- On top of the OPL layer 22 which extends out of the vias 12 and onto the oxide hard mask 14 are formed an oxide like over layer 24 , an anti-reflective layer 26 , and a photo-resist 28 .
- the photo-resist 28 has already been patterned and anti-reflective layer 26 and the OLO 24 have already been etched.
- the removal of the anti-reflective layer 26 material may be accomplished using chemistries including, for example, CF 4 , CF 4 /O 2 , and CF 4 /O 2 /Ar.
- the opening 23 formed in the photo-resist 28 sets the size for the subsequent openings that are etched into the anti-reflective layer 26 and the OLO layer 24 . As shown in FIG. 8 this opening is formed >20% smaller than the ultimate design rule for the IC design calls for.
- the opening 23 would be formed at approximately 80 nm, first in the photo-resist 28 and subsequently by etching in the anti-reflective layer 26 and the OLO layer 24 .
- FIG. 9 The effect of this shrinking the CD of the opening 23 , is shown in FIG. 9 , wherein anisotropic etching of the OPL layer 22 is undertaken.
- the anisotropic etching is used as it ensures vertical sidewalls to be formed in the OPL layer 22 .
- Etching chemistries for the OPL etch includes N 2 /CO 2 , N 2 /CO 2 /O 2 , and Ar/O 2 .
- the sidewalls are formed substantially in a straight line with the sides of the opening 23 and cause the OPL 22 not to be etched all the way to the via side walls 32 .
- V DC reactive-ion etch
- the CD was decreased from 145 to 118 to 100 nm by changing the V DC from 0 to 500 to 750 V DC .
- the design dimensions is 140 nm application of a 750V DC superposition during the RIE process would easily result in a reduction of the CD by approximately 32%
- Another method of changing the CD is to change an amount of CHF 3 used during the RIE process. In one embodiment, this is achieved by adjusting the proportion of polymerizing gases used in the plasma. It has been observed that as the ratio of CHF 3 to CF 4 is increased, more sidewall polymer is generated which decreases the size of the opening.
- Etch CD (nm) Site 0 CHF 3 20 CHF 3 40 CHF 3 1 91.9 85.0 76.2 2 93.6 86.2 77.5 3 91.0 85.2 80.5 4 83.2 79.9 74.4 5 88.0 86.1 78.8 6 88.4 83.1 75.3 7 89.6 82.8 76.1 8 91.5 84.1 78.3 9 90.5 82.6 77.8 Average 89.7 83.9 77.2 Accordingly, by adding more CHF 3 the size of the CD can be reduced.
- the OLO 24 may be etched such that it is tapered, though typically a taper may be formed as a result of the polymerization process, this is generally looked at as undesirable except as used to produce a taper in the via 12 .
- the instant process utilizes this taper formed on the OLO 24 to advantageously impact the process as will be described below.
- This tapering is in the direction of the center of the opening defined by the photo-resist 28 .
- Chemistries for opening the OLO include for example, C 4 F 8 /Ar, CF 4 /CH 2 F 2 /Ar, CF 4 /CHF 3 /Ar.
- Other possibilities exist for creating the taper including new reactive ion etching devices which are able shrink the critical dimension CD in a specified area and may be useful in undertaking the process described herein.
- FIG. 9 a The effect of this tapering of the oxide-like over layer 24 , is shown in FIG. 9 a , which much like FIG. 9 shows the process following anisotropic etching of the OPL layer 22 .
- the anisotropic etching is used as it ensures vertical sidewalls to be formed in the OPL layer 22 .
- the sidewalls are formed directly beneath the tapered portions of the OLO and cause the OPL not to be etched all the way to the via side walls 32 .
- FIG. 10 is a photograph showing the via 12 sidewalls 32 protected by the OPL layer following the via etch.
- any remaining organic material of the OPL is cleared away.
- an anisotropic etch stop removal process can be used to remove the etchstop at the bottom of the via 12 . This may be accomplished using chemistries including CF 4 /CH 2 F 2 /Ar/CO 2 , or N 2 or O 2 . This results in a trench and vias with minimal undercut after DHF clean as shown in FIG. 13 .
- FIG. 16 shows the trench only structure following subsequent hard mask removal, etch of the low-k dielectric, etch stop removal and ashing steps.
- the low-k dielectric 16 of the trench only structure is damaged through depletion of carbon in the sidewall material.
- the same process would occur twice in the via areas where its not protected by the OPL during at least some of these steps.
- the oxide like material 30 can then be removed as shown in FIG. 17 through dilute HF cleaning. Following the HF clean the size of the trench increases approximately 10-30% of the CD and thus then narrowing of the CD by the processes discussed above is fully compensated for.
- the use of the CHF 3 in the etching can be used first to reduce the size of the CD to prevent removal of all of the OPL layer from the via sidewall and thus reduce the damage to the sidewalls initially. Finally the damage layer in trench only structures are removed through cleaning using dilute HF which compensates for the initial reduction in the CD in the trench only portion of the IC.
- FIGS. 18 and 19 show the result of the OPL over etch described above in the scenario where a tapered OLO layer 24 is used.
- the over etch compensates a little bit for the decrease in the CD caused by the taper by removing any footing at the bottom of OPL and creates opening for the trenches at OLO step.
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Abstract
Description
- 1. Field of the Invention
- The present invention relates generally to the field of semiconductors, particularly to manufacturing methods for fabricating semiconductor devices, and more particularly to the Back-End-Of-Line (BEOL) semiconductor manufacturing process using via first dual damascene processes.
- 2. Description of the Prior Art
- The semiconductor manufacturing process, when likened to an assembly line, includes two major components, namely the Front-End-of-Line (FEOL) which includes the multilayer process of the actual forming of semiconductor devices (transistors, etc.) on a semiconductor substrate, and the Back-End-Of-Line (BEOL) which includes the metallization after the semiconductor devices have been formed. Like all electronic devices, semiconductor devices in a microchip such as an integrated circuit (IC) need to be electronically connected through wiring. In an integrated circuit, such wiring is done through multilayer metallization on top of the multilayered semiconductor devices formed on the semiconductor substrate. The complexity of this wiring becomes immediately appreciable once one realizes that there are usually hundreds of millions or more semiconductor devices (transistors in particular) formed on a single IC, and all these semiconductor devices need to be properly connected. This is accomplished by multilayer metallization, with each metallization layer designated as
Metal 1, Metal 2, so on, whereMetal 1 is the metallization layer closest to the underlying semiconductor devices to provide local connections among neighboring devices, and other metallization layers provide increasingly global connections from Metal 2 to the top metallization layer. Each metallization layer consists of a grid of metal lines sandwiched between dielectric layers for electrical integrity. Modern semiconductor manufacturing process can involve six or more metallization layers. - Although in the early years of semiconductor industry BEOL was generally less important than FEOL, the recent advancements have changed that equation. Microchip interconnect technology has become a critical challenge for future IC advancements due to the increasing difficulties to reduce signal propagation delay or interference caused by the increasingly dense interconnects. The problem is particularly acute considering that while an increase of metallization density means longer signal delays caused by the interconnects, a corresponding increase of transistor density means shorter signal traveling time between local semiconductor devices, making metallization increasingly a bottleneck in enhancing IC performance.
- Enhancements in integrated circuit (IC) density and performance as predicted by Moore's Law have fueled the semiconductor industry and resultant Information Revolution for over 40 years. The fabrication of deep submicron Ultra-Large Scale Integrated (ULSI) circuits requires long interconnects having small contacts and small cross-sections. In the past generation of semiconductor manufacturing process technology, aluminum (Al) and Al alloys have been used as conventional chip wiring materials while tungsten (W) has been used as contact plug between metal layers. The newer generation of the semiconductor manufacturing process technology has made it necessary to replace the Al technology with a technology based on a different metal. The introduction of copper (Cu) metallization served as an enabler for aggressive interconnects scaling due to its lower resistivity as compared with traditional Al metallization as well as improved reliability (such as less electromigration) and generally a reduced number of steps for fabrication.
- Developing along with the transition from Al to Cu has been the process of dual damascene etching. Unlike single damascene, dual damascene scheme forms vias and trenches for metal interconnect simultaneously. There are a number of different dual damascene schemes known and used. One such scheme is shown in
FIGS. 1-5 , where the process steps used to create a dual damascene interconnect structure using the via-first process scheme and the problems attendant thereto are shown. -
FIG. 1 shows a schematic cross section of a series of layers formed in the manufacture of anIC 10 prior to formation of vias therein. Thewafer 10's layers include asubstrate 11,metal lines 13, anetch stop layer 20, a low-kdielectric layer 16, an oxidehard mask 14, ananti-reflective coating 15, and a photo-resist 17. Using known etching and stripping processes, avia 12 is formed therein as shown inFIG. 2 . Thereafter, the photo-resist 17, theanti-reflective coating 15 is removed. This etching causes initial damage to thevia sidewalls 32. -
FIG. 3A , shows a portion of anIC 10 having a slightly more complex arrangement of layers than that ofFIGS. 1 and 2 , where thevia 12 has already been etched by the processes described above. This via 12 has been etched through an oxidehard mask 14, an inter-level dielectric layer (IDL) 16 (possibly a low-k or ultra low-k dielectric), and partially into theetchstop layer 20 with theIDL 16. Theintegration layer 18 is particularly necessary when using low-k or ultra low-k materials for theIDL 16 for better adhesion and reliability. As show inFIG. 3A , thevia 12 is filled with an organic planarizing layer (OPL) 22, which fills thevia 12 and covers thehard mask 14. Over theOPL layer 22 is formed a oxide-like overlayer (OLO) 24, ananti-reflective coating 26, and a photo-resist 28. Using lithography processes known to those of skill in the art apattern 30 for a trench is formed in the photo-resist 28. - The result of formation of the vias and trenches on the
wafer 10 are both horizontal and vertical via chains as shown inFIGS. 2B and 2C . - In
FIG. 3B shows the effect of etching using a CF4 chemistry. Namely, theanti-reflective coating 26 and the OLO 24 are etched through as well as a portion of theOPL 22. Next, the photo-resist 28 andanti-reflective coating 26 are removed and theOPL 22 is removed to a level below the oxidehard mask 14 using organic chemistry such as O2, CO2, H2 or N2 based chemistry, as shown inFIG. 3C . At this point a portion of thesidewall 32 of thevia 12 is exposed, this is highlighted in the circled portion ofFIG. 3C . - In
FIG. 3D the oxidehard mask 14 is opened to the size of the eventual trench. This is sometimes called a hard mask burn and can be accomplished by a fluorine based chemistry including for example, C4F8/Ar, CF4/CH2F2/Ar, CF4/CHF3/Ar, etc. As can be seen in the circled area ofFIG. 3D , the sidewall of thevia 12 is exposed to an even greater extent during this hard mask burn. This exposure of thesidewall 32 during the hard mask burn and subsequent steps effects the make up of thesidewall 32 and has a detrimental effect on the manufacture of the semiconductor. - In
FIG. 3E , a main etch is undertaken where thetrench 34 is formed. This is typically done using, for example, a CF4/Ar based chemistry. Again as a result of this step more of thesidewall 32 is exposed, which damage thesidewall 32. - In
FIG. 3F theOPL layer 22 is finally removed in its entirety using an O2 or H2 based chemistry. This step alone causes great damage to thesidewall 32. - Finally, in
FIG. 3G theetchstop layer 20 in the bottom of thevia 12 is removed using a CF4 or CH2 F2 based chemistry to complete thetrench 34 and via 12. The result of all of these etch steps and exposure of thesidewall 32 of thevia 12 to varying chemistries can be very dramatic because the next step after 3G is to send wafer for dilute hydrogen fluoride (DHF) clean step. This is wet clean step which actually removes all the damaged sidewall (oxide like layer).FIG. 7 c is a schematic representation of thewafer 10 followingfinal etch stop 20 removal and DHF clean showing the undercut of thehard mask 14. The undercut is produced at least in part by the ultimate removal of theILD 16 which has been damaged by the etching processes.FIG. 4 is a photograph of the undercut of thehard mask 14 over thesidewall 32 of the via 12, also called undercut. Much of this undercut is the result of removal of carbon depletion layer by DHF clean which is actually caused by the etching processes and is particularly troublesome when in low-k and ultra low-k dielectric applications and results in an increase in dielectric constant in theIDL 16. For example dramatic differences in the shape of the via can be seen by comparison ofFIG. 5 andFIG. 6 which show the unprotected via sidewall afterOPL layer 22 etch and followingfinal etchstop 20 removal plus DHF clean inFIG. 6 . - The undercut itself is a problem because it causes problem for the barrier layer deposition and hence prevents Cu from properly bonding to the via 12
sidewalls 32. This problem is shown inFIG. 7D . This improper bonding results in device reliability issues for devices manufactured using this process. Accordingly, there is a need for a dual damascene process that will overcome the shortcomings of the currently used processes such as those discussed above. - One aspect of the present invention is directed to a method of minimizing undercut of a hard mask in an integrated circuit (IC) structure including steps of providing an IC structure having a substrate, a interlayer dielectric layer, and a hard mask, forming a via in said IC structure, and depositing an organic planarizing layer (OPL) over the IC structure such that it fills the vias formed therein. The method also includes steps of forming a masking structure layer over the OPL, forming an opening in the masking structure that has a critical dimension (CD) smaller than an opening design dimension, anisotropic etching the OPL such that sidewall of the via remains covered with the OPL while forming a trench, and removing any remaining OPL on the sidewalls and trench, wherein the undercut of the sidewalls with respect to the hard mask is minimized by the covering of OPL during the anisotropic etching process.
- The present invention will now be described in more complete detail, with frequent reference being made to the figures identified below.
-
FIG. 1 is a schematic view of an IC prior to via etch; -
FIG. 2 is a schematic view of an IC following via etch using known techniques; -
FIGS. 2B-2C show horizontal and vertical via chains formed in an IC; -
FIGS. 3A-3G are a schematic representation of an IC undergoing dual damascene processing using known techniques; -
FIG. 4 is a photograph of a trench and via formed using dual damascene techniques, showing a hard mask undercut; -
FIG. 5 is a photograph of a via and trench structure after OPL etch with no protection of the via sidewall; -
FIG. 6 is a photograph of a via and trench structure with bad undercut; -
FIG. 7 a is a schematic representation of an IC showing a via structure formed using known techniques following further deposition OPL, OLO, anti-reflective layers, lithography of a photo resist layer and finish the dual damascene photo masking; -
FIG. 7 b is a schematic representation of the IC ofFIG. 7 a following etching, showing damaged ILD layer on the sidewalls of the trench and via structures; -
FIG. 7 c is a schematic representation of a via and trench structure formed using known techniques and having a hard mask undercut caused by removal of the damaged layer by dilute hydrogen fluoride (DHF) clean shown inFIG. 7 b; -
FIG. 7 d is a schematic representation of a via and trench structure showing the problem area for barrier metallization; -
FIG. 8 is a schematic view of an IC undergoing a first step in the method of the present invention with the CD decreased approximately 20% from the design dimension; -
FIG. 8 a is a schematic view of an IC undergoing a first step in a method of the present invention with the CD decreased by a taper formed in the OLO layer. -
FIG. 9 is a schematic view of an IC undergoing a second step in the method of the present invention; -
FIG. 9 a is a schematic view of an IC undergoing a second step in a method of the present invention with the CD decreased by a taper formed in the OLO layer; -
FIG. 10 is a schematic view of an IC undergoing a third step in the method of the present invention; -
FIG. 11 is a schematic view of an IC undergoing a fourth step in the method of the present invention; -
FIG. 12 is a schematic view of an IC undergoing a fifth step in the method of the present invention; -
FIG. 13 is a schematic view of an IC after undergoing a sixth and final step with dilute hydrogen fluoride (DHF) clean in the method of the present invention; -
FIG. 14 is a schematic view of a trench only portion of an IC undergoing the first step of the method of the present invention with the CD reduced by at least 20% from the design dimension; -
FIG. 15 is a schematic view of a trench only portion of an IC undergoing the second step of the method of the present invention where the OPL layer is over etched, removing any footing at the bottom of the OPL and creates an opening for the trenches which actually compensates for the reduction of CD at OLO step; -
FIG. 16 is a schematic of a trench only portion of an IC after undergoing etching, ashing, and etch stop removal showing damaged areas in the sidewall of the trench; -
FIG. 17 shows the trench only portion ofFIG. 17 following dilute HF cleaning to remove the damaged portion of the ILD layer; -
FIG. 18 is a schematic view of a trench only portion of an IC undergoing the first step of the method of the present invention with the CD reduced by a tapered OLO layer. -
FIG. 19 is a schematic view of a trench only portion of an IC undergoing the second step of the method of the present invention where the OPL layer is over etched to compensate for the reduction in CD caused by a tapered OLO layer. - As described above with reference to a known dual damascene process, via sidewalls are damaged during a via strip step, and then are further damaged by processing steps including the trench etch, etc. To minimize this damage, one aspect of the present invention is directed to a scheme which protects the sidewalls during the trench reactive ion etch (RIE) process, in a via first dual damascene process.
- In one aspect of the present invention, an etch sequence is used on masking structure for example an oxide-like over-layer (OLO) and an OPL integration scheme where the via sidewalls closest to the trench are protected by the OPL during OPL etch, an oxide hard mask open and main etches to avoid any unnecessary exposure to the sidewalls. In addition it has been found that this process does not affect the CD of trench only structures, having no via sidewalls to be concerned with.
-
FIG. 8 shows a cross section of a portion of anIC 10 in which vias 12 have already been formed. The portion of theIC 10 includes asubstrate 11, on whichmetal lines 13 have been formed. Anetch stop layer 20 covers themetal lines 13 and thesubstrate 11. AILD layer 16 covers theetch stop layer 20 and into which vias 12 have been formed, as described above with respect toFIGS. 1 and 2 . Thevias 12 are filled with anOPL layer 22. The top of theILD layer 16 is covered with ahard mask 14. On top of theOPL layer 22 which extends out of thevias 12 and onto the oxidehard mask 14, are formed an oxide like overlayer 24, ananti-reflective layer 26, and a photo-resist 28. As shown inFIG. 8 , the photo-resist 28 has already been patterned andanti-reflective layer 26 and theOLO 24 have already been etched. The removal of theanti-reflective layer 26 material may be accomplished using chemistries including, for example, CF4, CF4/O2, and CF4/O2/Ar. Theopening 23 formed in the photo-resist 28 sets the size for the subsequent openings that are etched into theanti-reflective layer 26 and theOLO layer 24. As shown inFIG. 8 this opening is formed >20% smaller than the ultimate design rule for the IC design calls for. Thus if an opening of 100 nm were called for by the design of theIC 10, then theopening 23 would be formed at approximately 80 nm, first in the photo-resist 28 and subsequently by etching in theanti-reflective layer 26 and theOLO layer 24. - The effect of this shrinking the CD of the
opening 23, is shown inFIG. 9 , wherein anisotropic etching of theOPL layer 22 is undertaken. The anisotropic etching is used as it ensures vertical sidewalls to be formed in theOPL layer 22. Etching chemistries for the OPL etch includes N2/CO2, N2/CO2/O2, and Ar/O2. The sidewalls are formed substantially in a straight line with the sides of theopening 23 and cause theOPL 22 not to be etched all the way to the viaside walls 32. - There are a variety of methods for changing the CD of the opening, such that the
OPL layer 22 is not etched to expose thesidewalls 32 of the via 12. One method utilizing the IC manufacturing equipment is direct current DC superposition during the reactive-ion etch (RIE) process. In this process the voltage VDC applied to one of the electrodes during the RIE process is varied to change the CD. The increase in VDC causes an increase in the plasma density within the reaction vessel. The change in plasma density helps to stimulate the polymerization chemistry while at the same time the plasma potential decreases which reduces the ion energy available for the reactive ion etch. - In one non-limiting example the CD was decreased from 145 to 118 to 100 nm by changing the VDC from 0 to 500 to 750 VDC. Thus in an instance where the design dimensions is 140 nm application of a 750VDC superposition during the RIE process would easily result in a reduction of the CD by approximately 32%
- Another method of changing the CD is to change an amount of CHF3 used during the RIE process. In one embodiment, this is achieved by adjusting the proportion of polymerizing gases used in the plasma. It has been observed that as the ratio of CHF3 to CF4 is increased, more sidewall polymer is generated which decreases the size of the opening.
- In one experiment, where all other parameters where kept constant, varying amounts of CF4/CHF3 were used. Initially, mixture of 150/0 CF4/CHF3 SCCM was used. Subsequently a mixture of 150/20 CF4/CHF3 SCCM was used. Finally a mixture of 150/40 CF4/CHF3 SCCM was used. Measurements were made at a total of nine locations in each test. The results were as follows.
-
Etch CD (nm) Site 0 CHF 320 CHF3 40 CHF 31 91.9 85.0 76.2 2 93.6 86.2 77.5 3 91.0 85.2 80.5 4 83.2 79.9 74.4 5 88.0 86.1 78.8 6 88.4 83.1 75.3 7 89.6 82.8 76.1 8 91.5 84.1 78.3 9 90.5 82.6 77.8 Average 89.7 83.9 77.2
Accordingly, by adding more CHF3 the size of the CD can be reduced. Those of skill in the art will appreciate that other combinations of polymerizing gasses may also be used including but not limited to C4F8/Ar, CF4/CH2F2/Ar, CF4/CHF3/Ar, and others, also the exact combination of gasses may vary depending upon the material of theOPL layer 22. - Alternatively, as shown in
FIG. 8 a, theOLO 24 may be etched such that it is tapered, though typically a taper may be formed as a result of the polymerization process, this is generally looked at as undesirable except as used to produce a taper in the via 12. In contrast, the instant process utilizes this taper formed on theOLO 24 to advantageously impact the process as will be described below. This tapering is in the direction of the center of the opening defined by the photo-resist 28. Chemistries for opening the OLO include for example, C4F8/Ar, CF4/CH2F2/Ar, CF4/CHF3/Ar. Other possibilities exist for creating the taper including new reactive ion etching devices which are able shrink the critical dimension CD in a specified area and may be useful in undertaking the process described herein. - The effect of this tapering of the oxide-like over
layer 24, is shown inFIG. 9 a, which much likeFIG. 9 shows the process following anisotropic etching of theOPL layer 22. The anisotropic etching is used as it ensures vertical sidewalls to be formed in theOPL layer 22. The sidewalls are formed directly beneath the tapered portions of the OLO and cause the OPL not to be etched all the way to the viaside walls 32. - Next, as shown in
FIG. 10 , the main trench etch is undertaken, again using an anisotropic process, with the result being that the sidewalls of the via 12 are not actually affected by the etch. This etch may be accomplished using chemistries include C4F8/Ar/N2, CF4/Ar, CF4/CH2F2/Ar/O2, CF4/CHF3/Ar/O2 etch.FIG. 10 a is a photograph showing the via 12sidewalls 32 protected by the OPL layer following the via etch. - In
FIG. 11 , by using a low pressure stripping method, followed by an over ash with a high pressure process, or wet cleans and solvents, any remaining organic material of the OPL is cleared away. Finally, as shown inFIG. 12 an anisotropic etch stop removal process can be used to remove the etchstop at the bottom of the via 12. This may be accomplished using chemistries including CF4/CH2F2/Ar/CO2, or N2 or O2. This results in a trench and vias with minimal undercut after DHF clean as shown inFIG. 13 . - By using such a scheme for forming the
vias 12 andtrenches 34 without damaging the sidewalls of the vias, one may believe that in a trench only portion of theIC 10, the dimension of such a trench might be reduced. This might be expected because the CD of the trench would appear to have been reduced by, for example, 20% using the preceding processes. However, experience shows that following the OLO etch shown inFIG. 14 of a trench only structure, the OPL etch in the trench only area sees more over etch which actually opens the bottom of trench (with no footing) and compensates for the CD which was reduced after the OLO open step. This is due to the selectivity of the OPL etching materials to oxide hard mask and despite their anisotropic nature, upon reaching thehard mask 14, the OPL layer is opened laterally to compensate a little bit of the CD shrink caused by the tapering of the OPL layer. -
FIG. 16 shows the trench only structure following subsequent hard mask removal, etch of the low-k dielectric, etch stop removal and ashing steps. As a result of these steps, the low-k dielectric 16 of the trench only structure is damaged through depletion of carbon in the sidewall material. Turning it into an oxide-like material 30. The same process would occur twice in the via areas where its not protected by the OPL during at least some of these steps. The oxide likematerial 30 can then be removed as shown inFIG. 17 through dilute HF cleaning. Following the HF clean the size of the trench increases approximately 10-30% of the CD and thus then narrowing of the CD by the processes discussed above is fully compensated for. - This increase in trench size in the trench only portion of the
IC 10 through the dilute HF clean is another portion of the equation in regulating the changes in CD following the initial reduction described above to protect the sidewalls of the trench. Using the two similar processes described above where the etching is done with a combination of CF4/CHF3 in a ratio of 150/x sccm, the damage to the sidewalls, which is subsequently removed as shown inFIGS. 16 and 17 , can be determined. Inprocess 1, 0 CHF3 was used and in process 2, 40 CHF3 was used. -
Process 1 with 0 CHF3CD Process 2 with 40 CHF3 Etch after DHF 40 CD after DHF CD Clean Damage CHF3 Clean Damage 1 91.9 106.7 14.8 76.2 112.1 35.9 2 93.6 109.0 15.4 77.5 108.3 30.8 3 91.0 109.4 18.4 80.5 103.6 23.1 4 83.2 102.1 18.9 74.4 102.7 28.3 5 88.0 104.8 16.8 78.8 98.8 20.0 6 88.4 102.3 13.9 75.3 100.2 24.9 7 89.6 103.2 13.6 76.1 97.9 21.8 8 91.5 105.3 13.8 78.3 95.3 17.0 9 90.5 103.0 12.5 77.8 93.7 15.9 Average 89.7 105.1 15.3 77.2 101.4 24.2 - By the foregoing example, the use of the CHF3 in the etching can be used first to reduce the size of the CD to prevent removal of all of the OPL layer from the via sidewall and thus reduce the damage to the sidewalls initially. Finally the damage layer in trench only structures are removed through cleaning using dilute HF which compensates for the initial reduction in the CD in the trench only portion of the IC.
-
FIGS. 18 and 19 show the result of the OPL over etch described above in the scenario where a taperedOLO layer 24 is used. As before, the over etch compensates a little bit for the decrease in the CD caused by the taper by removing any footing at the bottom of OPL and creates opening for the trenches at OLO step. - The above description, including the specification and drawings, is illustrative and not restrictive. Many variations of the invention will become apparent to those of skill in the art upon review of this disclosure. Various features and aspects of the above-described disclosure may be used individually or jointly. Further, the present disclosure can be utilized in any number of environments and applications beyond those described herein without departing from the broader spirit and scope of the specification. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents. In addition, it will be recognized that the terms “comprising,” “including,” and “having,” as used herein, are specifically intended to be read as open-ended terms of art. The term “or” as used herein is not a logic operator in an exclusive sense unless explicitly described as such.
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SG201101373-7A SG170038A1 (en) | 2007-09-28 | 2008-08-19 | Method of minimizing via sidewall damages during dual damascene trench reactive ion etching in a via first scheme |
SG200806130-1A SG151170A1 (en) | 2007-09-28 | 2008-08-19 | Method of minimizing via sidewall damages during dual damascene trench reactive ion etching in a via first scheme |
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US20140027915A1 (en) * | 2012-07-24 | 2014-01-30 | Infineon Technologies Ag | Production of adhesion structures in dielectric layers using photoprocess technology and devices incorporating adhesion structures |
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US9466525B2 (en) * | 2012-09-21 | 2016-10-11 | Taiwan Semiconductor Manufacturing Company, Ltd. | Interconnect structures comprising flexible buffer layers |
US20160358820A1 (en) * | 2015-05-13 | 2016-12-08 | International Business Machines Corporation | Via formation using sidewall image tranfer process to define lateral dimension |
US10157789B2 (en) * | 2015-05-13 | 2018-12-18 | International Business Machines Corporation | Via formation using sidewall image transfer process to define lateral dimension |
US11393715B2 (en) * | 2019-09-30 | 2022-07-19 | Shanghai Huali Integrated Circuit Corporation | Method for manufacturing a 14nm-node BEOL 32nm-width metal |
US11398409B2 (en) | 2020-09-22 | 2022-07-26 | International Business Machines Corporation | Method of forming a BEOL interconnect structure using a subtractive metal via first process |
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SG151170A1 (en) | 2009-04-30 |
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